Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.49   5.526%   $62.7774   $62.78   $62.80   $62.80  
  Purchase #2 $246.50   12.380%   $277.0167   $277.02   $277.00   $277.00  
  Purchase #3 $193.89   4.113%   $201.8647   $201.86   $201.85   $201.90  
  Purchase #4 $49.32   10.806%   $54.6495   $54.65   $54.65   $54.60  
  Purchase #5 $46.29   10.488%   $51.1449   $51.14   $51.15   $51.10  
  Purchase #6 $142.94   3.548%   $148.0115   $148.01   $148.00   $148.00  
  Purchase #7 $184.97   7.461%   $198.7706   $198.77   $198.75   $198.80  
  7 purchase totals = $923.40       $994.2353   $994.23   $994.20   $994.20